Materials suitable for such applications as electrical insulation, heat insulation, sound insulation, and decorative building elements consisting essentially of ceramic fibers bonded into an article of a desired geometry utilizing an organic or inorganic binder have been marketed commercially for many years. Depending upon the destined application, which can range from acoustic ceiling tile to wrappings for liquid-carrying pipes, the ceramic fibers employed have included such widely-varying materials as asbestos, calcium sulfate, fiber glass, mica, perlite, cellulose, and mineral wool, to name but a few of the most common.
It is quite apparent that the strength imparted to the final article by the binder is of great significance. The chemical durability and weathering resistance of the binder are also highly important and, where highly elevated temperatures are to be experienced, the binder must demonstrate sufficient refractoriness and heat stability. The use of an inorganic binder generally removes the threat of flammability inherent in the use of organic bonding media.
U.S. Pat. No. 4,239,519 discloses the production of inorganic, crystal-containing gels which perform as precursors for the preparation of papers, fibers, films, boards, and coatings. The patented method for developing the gels contemplates three basic elements: first, a fully or predominantly crystalline body (most preferably a glass-ceramic body) is formed which contains crystals consisting essentially of a lithium and/or sodium water-swelling mica selected from the group of fluorhectorite, hydroxyl hectorite, boron fluorphlogopite, hydroxyl boron phlogopite, and solid solutions among those and between those and other structurally-compatible species selected from the group of talc, fluortalc, polylithionite, fluorpolylithionite, phlogopite, and fluorphlogopite; second, that crystalline body is contacted with a polar liquid, customarily water, to cause swelling and disintegration of the body accompanied with the formation of a gel; and, third, the solid:liquid ratio of the gel is adjusted to a desired value depending upon the utility to which the final product is to be placed.
The crystals developed following the disclosure of U.S. Pat. No. 4,239,519 demonstrate a morphology of a continuum of flakes, rectangular-like strips, and interwoven ribbons in parallel or sub-parallel zones or sheaths with said flakes being irregularly shaped with diameters between about 0.5-10 microns and cross sections of less than 100 .ANG., and said strips and ribbons being about 0.5-10 microns long, about 500-5000 .ANG. wide, and less than about 100 .ANG. thick. That morphology yields crystals displaying a very high aspect ratio, higher than naturally-occurring mica, and large surface area, both of those characteristics rendering the materials useful for reinforcing various matrices.
Good chemical durability is endowed to the papers, fibers, films, boards, coatings, etc., prepared from the gels by contacting those products with a source of large cations to effect flocculation of the gel and an ion exchange reaction to occur between the large cations and the Li.sup.+ and/or Na.sup.+ ions from the interlayer of the crystals, and then washing and drying the resulting materials. The patent observed the utility of K.sup.+, Rb.sup.+, Cs.sup.+, Ag.sup.+, Cu.sup.+, NH.sub.4 .sup.+, H.sub.3 O.sup.+, Ca.sup.+2, Sr.sup.+2, Ba.sup.+2, Pb.sup.+2, and certain organic polycations, specifically reciting aniline hydrochloride and quaternary ammonium compounds as illustrative of operable large cations.
If desired, the ion exchange reaction may be carried out with the gel, i.e., before paper, fibers, films, boards, coatings, or other products are formed therefrom, or it may be conducted during the actual forming process for the product. However, no matter at what juncture the ion exchange reaction is undertaken, its occurrence is unequivocally required to prevent spontaneous degradation of the products in the presence of water.
Where products produced in accordance with that patent have been subjected to long term testing, it has been discovered that such physical properties thereof as mechanical strength, dielectric strength, loss tangent, and ionic conductivity are deleteriously affected by an atmosphere of high relative humidity. Thus, the physical characteristics exhibited by those products are not permanently stable in the presence of moisture.
U.S. application Ser. No. 461,672, filed concurrently herewith in the name of Shy-Hsien Wu under the title ORGANIC-INORGANIC COMPOSITES OF NEUTRALIZED POLYELECTROLYTE COMPLEXES now U.S. Pat. No. 4,455,382 and U.S application Ser. No. 461,571, also filed concurrently herewith in the names of S. N. Hoda and A. R. Olszewski under the title ORGANIC-INORGANIC COMPOSITES CONTAINING SYNTHETIC MICA, now U.S. Pat. No. 4,454,237 have for their objectives the development of means for rendering products produced in accordance with the method of U.S. Pat. No. 4,239,519 relatively insensitive to changes in relative humidity in the surrounding environment.
The basis of the first disclosure lies in the discovery that a neutralized polyelectrolyte complex can be prepared via the reaction of an anionic gel prepared in the manner described in U.S. Pat. No. 4,239,519 with an equivalent amount of an organic polycation. Such a complex, when formed into paper, fiber, film, board, or coating, displays exceptional toughness, excellent hydrophobicity, high mechanical strength, and good electrical properties. And, because of the resistance of the products to attack by moisture, the physical characteristics thereof are quite insensitive to variations in relative humidity of the atmospheres to which they are exposed. The exceptional hydrophobic character exhibited by the products of Ser. No. 461,672 is acquired through the formation of a strong polycation-polyanion interaction. Moreover, the long chain nature of a polycation imparts high strength and toughness to the composites, since the polycation can react with itself and/or with adjoining chains upon curing.
As is mentioned in Ser. No. 461,672 , ion exchange of an organic polycation with an anionic gel was cursorily alluded to in U.S. Pat. No. 4,239,519. Nevertheless, there was no teaching in the patent of the criticality for maintaining charge neutrality in the exchanged system. In contrast, charge neutrality comprises the very crux of the inventive materials disclosed in Ser. No. 461,672. That is, each of the exceptionally desirable chemical and physical properties exhibited by the inventive materials can be laid to the organic polycations reaction with an equivalent quantity of inorganic polyanions' (gels) to form a neutralized polyelectrolyte complex. In sum, any significant movement away from charge neutrality yields a polyelectrolyte complex system which is virtually of no practical utility because of its high sensitivity to deterioration in a moisture-laden environment.
The inventive method disclosed in Ser. No. 461,672 to produce paper, fiber, film, board, or coating involves six general steps:
(a) a fully or predominantly crystalline body is prepared according to the practice described in U.S. Pat. No. 4,239,519 and having an overall composition and microstructure as disclosed in that patent;
(b) that body is contacted with a polar liquid, customarily water, for a period of time sufficient to cause swelling and disintegration thereof accompanied with the formation of a gel having crystals dispersed therewithin;
(c) that gel is contacted with a source of organic polycations in an amount and for a time sufficient to cause an ion exchange reaction to take place between the organic polycations and the Li.sup.+ and/or Na.sup.+ ions from the interlayer of the above-noted crystals and to neutralize the charge density of those crystals, thereby promoting the formation of a neutralized polyelectrolyte complex;
(d) that complex, normally existing in the form of floc, is dispersed into a liquid selected from the group of polar organic liquids, aqueous NH.sub.4 OH solutions, and aqueous salt solutions of large cations selected from the group of K.sup.+, Rb.sup.+, Cs.sup.+, Ag.sup.+, Cu.sup.+, NH.sub.4.sup.+, Ca.sup.+2, Sr.sup.+2, and Pb.sup.+2 ;
(e) the solid:liquid ratio of the complex and liquid is adjusted to a desired fluidity; and
(f) paper, fiber, film, board, or coating is prepared therefrom.
Formamide is noted as being the preferred organic liquid dispersing solution and aqueous solutions of KC1 and NH.sub.4 OH as the preferred inorganic dispersants.
Ser. No. 461,672 discloses and describes three categories of organic cations which are operable in that invention, viz., N.sup.+, P.sup.+ and S.sup.+. The most common of those is N.sup.+, of which there are four types:
(1) a primary amine solubilized with acid, exemplified by EQU R--NH.sub.3.sup.+ X.sup.- ;
(2) a secondary amine solubilized with acid, illustrated by ##STR1##
(3) a tertiary amine solubilized with acid, represented by ##STR2##
(4) a quaternary ammonium acid salt, designated by ##STR3## wherein the cationic characteristic increases from the primary amine up to the quaternary cation.
Illustrative of the P.sup.+ cation is the quaternary phosphonium acid salt ##STR4##
The S.sup.+ cation is represented by the ternary sulfonium acid salt ##STR5##
The most preferred source of organic polycations disclosed in Ser. No. 461,672 is stated to be KYMENE 557H solution, marketed by Hercules, Incorporated. That material is described as a cationic, water soluble condensate of a basic polyamide and epichlorohydrin which has assumed a polyamide-polyamine-epichlorohydrin resin form. Other operable polyquaternary ammonium salts cited in Ser. No. 461,672 include ACCOSTRENGTH 711, marketed by American Cyanamid Company, Wayne, N.J., and NALCOLYTE 7134, marketed by Nalco Chemical Company, Chicago, Ill.
The inventive method disclosed in Ser. No. 461,571 to produce composite articles of various geometries such as paper, fiber, film, board or coating utilizes five general steps:
(1) a fully or predominantly crystalline body is formed according to the method disclosed in U.S. Pat. No. 4,239,519 and having an overall composition and microstructure as defined in that patent;
(2) that body is contacted with a polar liquid, conveniently water, for a period of time sufficient to cause swelling and disintegration thereof accompanied with the production of a gel having crystals dispersed therewithin;
(3) that gel is contacted with a source of organic cations selected from the group of aminosilanes and organic chrome complexes in an amount and for a time sufficient to cause an ion exchange reaction to take place between said cations and Li.sup.+ and/or Na.sup.+ ions from the interlayer of said crystals;
(4) the solid:liquid ratio of the exchanged gel and the liquid is adjusted to a desired fluidity; and
(5) paper, fiber, film, board, or coating is prepared therefrom.
Ser. No. 461,571 discloses Z6020, N-.beta.-aminoethyl-.gamma.-aminopropyl trimethoxy silane, marketed by Dow Corning Corporation, Midland, Mich., as illustrative of an operable aminosilane, and teaches suitable organic chrome complexes as being selected from the group of a chemically reactive Werner complex, methacrylato chromic chloride, wherein methacrylic acid is coordinated with chromium (VOLAN), and a chemically reactive Werner complex wherein a C.sub.14 -C.sub.18 fatty acid is coordinated with trivalent chromium (QUILON C), both marketed by E. I. DuPont de Nemours & Co., Wilmington, Del.
U.S. Pat. No. 4,239,519 is primarily concerned with the use of glass-ceramics as starting materials for producing crystal-containing gels. Several other means for producing operable starting materials are available, however.
For example, "Fluorine Micas", Bureau of Mines Bulletin 647, pages 236-242 (1969) describes sintering and recrystallizing a batch composed of raw materials such as talc, silica, magnesia, and fluoride in the proper proportions to form water-swelling fluormicas that can be utilized to make inorganic paper.
As an alternative to that simple reaction sintering practice, a synthetic lithium and/or sodium water-swelling, gel-forming material can be prepared by firing a batch of a predetermined composition in an autoclave. As illustrative of that technique, a lithium fluormica can be produced by hydrothermally treating a batch compounded from talc, a source of silica such as silicic acid or powdered silica, lithium silicate, magnesia, lithia, and fluorides of lithium, magnesium, or ammonium in the proper proportions to yield the stoichiometry of the desired lithium fluormica.
In yet another method, magnesium and silica-containing species are co-precipitated in the presence of Li.sup.+, Na.sup.+, and F.sup.- ions and that precipitate subjected to a hydrothermal treatment. In a variation of that technique, SiO.sub.2 is precipitated into a preformed aqueous suspension of a water insoluble magnesium compound. That mass is then subjected to a hydrothermal treatment in the presence of excess lithium or sodium compounds.
As can be observed, each of those methods requires the batch constituents to be present in such amounts that the reaction product will approximate a desired stiochiometry.